The present invention relates to an ergonomic chair adjustable as to the height having a seat front portion tiltable as a function of said height adjustment.
It is known that chairs or armchairs for use in an office or the like are often provided with a function allowing the height of a seat portion to be freely changed in accordance with the physique of a sitting person, the height of a desk employed and so forth. It is known as well that chairs having a swingable backrest exist in which a seat front portion can be tilted downwards, thus avoiding the raising of the user's legs, either in a suitable adjustable way, or because said portion is hinged freely with respect to the rest of the seat and it can be lowered by means of a certain pressure exerted by a lower region of the thighs of the user himself. There are also chairs in which a seat front portion is permanently tilted downwards with a fixed angle, but clearly without any utility, as it results in a shorter seat, i.e. lacking said front portion.
From WO-A-8906101 of the present applicant another ergonomic chair is known, adjustable in height, in which the tilting angle of the whole seat changes as a function of the seat height by swinging along an arc of circumference about a center of rotation substantially coincident with the center of gravity of a person sitting on the chair itself. In that case the effect is very comfortable, however the problem remains unsolved in that, as the slope of the whole seat with respect to the backrest is changed as a function of the height of the seat itself, the user is necessarily caused to exert, in case of considerable tilting angles, a certain force on the rest areas in order to avoid a downward sliding along an inclined plane formed by the seat itself, in spite of the fixed position of the center of gravity. Thus the user must exert a pressure both on the floor by his feet and on the seat rear portion by his ischial region in order to stay in a balanced position, which may involve some discomfort and a non-negligible fatigue.
U.S. Pat. No. 4,521,053 discloses a chair whose seat is adjustable as to the height and which is formed in two portions, the front portion of which is downwardly tiltable with respect to the rear portion to which it is hinged. However, the tilting angle is to be chosen at will by the user who has to exert a pressure on the front part of the seat with his thighs until finding the preferred, most comfortable tilting angle.
It is also known that a great number of chairs, especially for use in an office and particularly suitable for typists and computer operators, or also for meeting-rooms and the like, have a backrest adjustable as to the height to keep correct, in accordance with the user's stature, the resting of the back, which takes place in the lumbar vertebrae region. By means of ergonomic research it was found that such height corresponds to a third of the height of a sitting person's trunk.
It is also known that the armrests of the chairs having same are preferably adjustable in height, either integrally to each other or independently, in order to ensure a correct leaning of the sitting person's elbows. However, it is necessary, to the aim of reaching an ergonomically valid result and to avoid uncomfortable postures, which are tiring so as to cause, in time, physical malformations, that the armrests adjustment is combined with a backrest adjustment as a function of the stature of the chair user. Naturally it is not easy to adjust armrests and backrests separately, based on both the difficulty of the operation to be executed, and the uncertainty of the obtained result, which often can involve additional adjusting operations.